Level gages are used to determine liquid levels in tanks. A sight glass positioned on the outside of the tank is suitable for many applications. Other types of level gages for tanks generally rely on electronics and/or a float for operability, and can have components positioned inside or outside of the tank.
An advantage of an electronic gage is that the level reading can be instantaneously transmitted to a remote location for a continuous level readout. The electronic level signal can also be used in automated process control. A disadvantage is that components of an electronic gage can fail or require servicing, necessitating their removal.
Since many tanks are provided on their upper ends with flanged nozzles or access ports, or can be easily provided with one, a level gage which could be installed vertically on a flanged opening would be easy to install. Because the ports or nozzles are sometimes of small diameter, a level gage transmitter capable of being installed in a small diameter port would be very desirable, since it could be installed with minor accommodation in larger diameter ports simply by carrying it on a plate sized to fit the flange.
For some types of service, such as where the tank may contain a head of toxic or flammable vapors, or be at elevated pressures, or have need to remain hermetically sealed such as for uses in the pharmaceutical or food services industries, a level gage system which permitted the electronics components of the gage to be removed from the tank while maintaining a hermetic seal on the tank would be very desirable.